1. Field of the Invention
The present invention relates to methods and apparatus for controlling production of fluids from a well and, more particularly, to such methods and apparatus wherein produced well fluids are introduced into a vessel wherein the fluids separate into gas and liquid phases.
2. Setting of the Invention
A typical arrangement for handling fluids which are produced from an oil and gas well includes a transfer vessel in which the produced fluids separate into their liquid and gas phases. The transfer vessel includes an outlet at the upper end thereof which is connected to a gas sales line via a pressure control valve. The lower end of the tank includes an outlet connected to a pump for pumping the liquids from the transfer vessel for processing and/or storage. A liquid level monitor senses the level of the liquid in the tank and turns the pump on when the vessel liquid rises above a preselected level and shuts the pump off when the vessel liquid falls below a preselected level.
In the event of a transfer pump failure, the liquid level in the tank rises above the upper preselected level at which the pump is normally activated. An emergency condition sensor detects the abnormal rise in liquid level and opens a gas-actuated valve which is connected to an emergency liquid drain on the vessel. After the emergency valve opens, the gas pressure in the tank boosts the liquid into the emergency drain, which is connected to a set of storage tanks for temporarily storing the produced liquids.
It should be noted that there must be sufficient gas pressure in the vessel to force the liquid in the vessel into the emergency drain. The pressure control valve in the gas sales conduit is adjusted to maintain sufficient pressure to boost liquids into the tank in the event of a pump failure. The gas pressure in the vessel is communicated to the wellbore via the line which provides the produced well fluids to the vessel. A problem exists in that when the pressure in the transfer vessel is maintained at a level sufficient to drain liquid therefrom in the event of a pump failure, the pressure is also sufficient to slow the flow of fluid production from the well. When the well pressure is sufficiently low, the vessel backpressure which is communicated to the well can significantly retard the flow of fluids form the well into the transfer vessel.
There exists a need for a method and apparatus for controlling production of fluids from a well in which the backpressure communicated to the well from the transfer vessel is significantly reduced.